The present invention relates to an image processing apparatus that is preferably applied to a facsimile device, and more particularly to an image processing apparatus in which the number of notches (unprinted pixels in a line of printed pixels) can be reduced.
For example, in a facsimile device, the following operations are generally performed: image data which has been read in an image reading section, is converted into bi-level data in accordance with a predetermined threshold value; the converted data is appropriately coded; and the coded data is transmitted to the other party.
When image data is converted into bi-level data, notch N shown in FIG. 5 occurs frequently due to the fluctuation of the system.
As can be seen from FIG. 5, notch N is defined as follows: on a boundary between 0 and 1 bi-level data, one pixel data on one side is projected to the other side. When the aforementioned notch N is caused, the correlation of data in the longitudinal or lateral direction is interrupted, so that the coding efficiency is lowered. Accordingly, a long period of corresponding time is required.
In order to solve the aforementioned problems, various image processing methods to remove notch N have been proposed. For example, according to one method carried out before binarization, a smoothing filter such as a median filter is used. Further, according to another method carried out after binarization, pattern matching is conducted.
When the median filter is adopted, the number of notches N can be reduced, however, its effect is small. Further, in the case where fine lines are included in a window, they can not be recognized. That is, the original data is lose by the filtering operation, and the resolution is deteriorated.
The method of pattern matching is carried out after binarization. Therefore, this method is not appropriate to process multi-level data.
The present invention has been achieved to solve the aforementioned problems. It is a primary object of the present invention to provide an image processing apparatus which can positively prevent the occurrence of notches during the process of binarization and further prevent the deterioration of resolution.